The invention relates to a button holing sewing machine. The invention relates more particularly to a needle thread guiding apparatus which guides the needle thread so that it is not stuck by the needle during the button holing process.
Referring now to FIGS. 4 and 7 of the drawings, a conventional button holing sewing machine is shown. A needle bar 1 holds a needle 2 at its lower end, it in turn is held by a needle bar frame 3 and can be moved up and down therefrom. The upper end of the needle bar frame 3 is pivoted by means of a hinge stud 5 affixed to the frame 4.
A guide block 7 is slidably inserted into a groove portion 6. The guide block 7 is pivoted by a pin which is projected from a rock arm 8.
The rock arm 8 is oscillated by the rock shaft which is connected to the needle oscillation mechanism located rear side of the sewing machine. The oscillation mechanism comprises a triangle cam inserted in a needle bar pitman. Such a mechanism is well known.
Thus the needle bar frame 3 oscillates around the hinge stud 5. To keep this oscillating motion more stable, a guide plate 9 is provided such that the needle bar frame 3 slides along the guide plate 9. The guide plate 9 is fixed to the machine frame 4. A presser foot 11 is connected to one end of a work clamp 12. Another end of this work clamp 12 is connected to a work-clamp-arm-slide-rod 13.
The work-clamp-arm-slide-rod 13 is slidably inserted into a support 14. An arm 15 is connected to the work-clamp-arm-slide-rod 13. A link 16 is connected to a feed-regulating-scale-arm 17 by a screw 18. The feed-regulating-scale-arm 17 is connected to a feed link 20 by means of a rotational shaft 19. The feed link 20 is rotatably connected to a roller 21a which is slidably inserted into a groove 21 provided at the bottom surface of a feed cam 50.
Incorporating the rocking motion of the rock arm 8, the needle bar 1 is oscillated as shown in arrow "A" (FIG. 4). The rotational motion of the groove 21 by the feed cam 50 causes the feed-regulating-scale-rod 17 to oscillate around the rotational shaft 19. Thus, the work-clamp-arm-slide-rod 13 slides along the shaft hole of the support 14 by means of the link 16 and the arm 15. Accordingly, the presser foot 11 moves in the direction shown in arrow "B" (FIG. 4) by means of the work clamp 12. Such a mechanism of the button holing sewing machine is well-known.
Under the conventional button holing sewing machine, described above, the needle bar frame 3, causes the needle 2 to oscillate, and the presser foot 11, which is connected to the work clamp 12, feeds the workpiece in the direction of "C" and "D" as shown in FIG. 5, and thus the staggered stitch line 23 is conducted and the button holing sewing machine completes one cycle of stitching.
FIGS. 6A, 6B, 8A and 8B of the drawings illustrate a conventional button holing sewing machine and the positional relationship between the direction of threading into the needle eye and the position of the operator.
A needle eye 2a is threaded by a needle thread 24 which has a portion of a needle thread 24a which is positioned above the needle eye 2a, and a portion of needle thread 24b which is positioned below the needle eye 2a and an operator's position M is shown in FIGS. 8A and 8B. Under such a positional relationship, as shown in FIGS. 8A, 8B and 5, when a workpiece 22 is fed in the direction of "D" (FIG. 8A), the needle thread portion 24b positioned below the needle eye 2a is positioned toward the operator's side in relation to the needle's position as shown in FIG. 6A and FIG. 8A.
By contrast, when the workpiece 22 is fed in the direction of "C" (FIG. 8B), the needle thread portion 24b positioned below the needle eye 2a is positioned partly toward the rear side of the needle and away from the operator's side as shown in FIGS. 6B and 8B. Therefore, it is possible that the needle 2 sticks the needle thread portion 24b when the needle 2 descends, thereby cutting the needle thread 24.